To make driving more comfortable in winter or in cold climate, vehicles can include a heatable steering wheel, in addition to an air heater and a seat heater. Typically, the steering wheel rim includes a resistance heating element comprised of a heating wire. A heatable steering wheel is normally offered in luxury vehicles, which have a plush matching interior, typically include matching wood and leather. These materials, however, are not particularly suitable for transmitting heat because wood and leather are poor heat conductors. Indeed, a wooden steering wheel rim is generally thick, making it unsuitable for heating.
In this respect, German patent publication DE 297 12 839 discloses simplifying the production of a heatable steering wheel by injection molding conductive plastic shells onto its steering wheel rim. The conductive plastic acts as a resistance heating element. Wood and leather are used to dress the rim of a luxury vehicle. Accordingly, this reference still does not solve the non-uniform heating problem associated with these materials. Similar heating problems relating to uniformity and heating speed occur with a steering wheel rim encased with film or lacquer.
Accordingly, there is a need for a heatable steering wheel that can heat poor conductive materials used for covering the steering wheel rim. The present invention addresses this need.
The present invention relates to a heatable steering wheel, a heatable steering wheel rim thereof, and a method of heating a steering wheel.
One aspect of the invention is a steering wheel rim, which can comprise a steering wheel rim core, an outer casing, and a heating device for heating the outer casing. The other aspect of the invention is a steering wheel that can include the above-described steering wheel rim. The steering wheel can include a steering wheel hub and spokes that connect the steering wheel rim to the hub. The heating device also can heat portions of the spokes.
The core can include a frame, which can be circular, and an insulating layer formed around the frame. The insulating layer can completely or substantially encapsulate or surround the frame. The heating device can include a layer of electrically conductive plastic surrounding the core, or resistance plates formed over the core, and a pair of electrodes extending along the length of the conductive layer or the resistance plate. More specifically, the electrodes can extend substantially along the entire peripheral length of the conductive or insulating layer, and the conductive layer can encapsulate the insulating layer and the electrodes. The rim can include an outer casing surrounding the conductive layer. The conductive layer heats the outer casing, which can be a decorative layer comprised of one or more of wood, leather, film, and lacquer, when current flows through the electrodes.
The electrodes are positioned along the conductive layer to allow current to uniformly pass along the periphery of the steering wheel rim into the conductive layer. The conductive layer can be configured as a plastic shell that at least partially fits around the core. The conductive layer also can completely surround the core. The conductive layer can be comprised of two half shells connected together over the core. The two half shells can be joined together by ultrasonic or electromagnetic welding. At least one of the half shells can include a securing projection for fastening to the core or the insulating layer. The conductive layer also can be comprised of at least two segments, which can be separately heated or only one of which is heatable. The conductive layer can be injection molded over the core to encapsulate the electrodes and the core.
The electrodes can be strip conductors extending along the periphery of the core. The electrodes can be spaced from each other in the radial direction or transversely thereof relative to the steering wheel rim. The electrodes can be substantially spaced apart diametrically opposite the core. A portion of the steering wheel frame can comprise one of the electrodes. Moreover, at least one of the electrodes can be comprised of copper strands or a perforated or profiled metal strip.
Another aspect of the present invention is the method of heating a steering wheel rim having a structural core. The method can include the steps of placing the pair of electrodes substantially diametrically opposite the core, surrounding the electrodes and the core with an electrically conductive plastic layer, and flowing current through the electrodes to distribute current to the electrically conductive plastic layer and heat the same. The electrodes extend along the length of the conductive layer. The method can include or more features of the steering wheel described above.